Granata KP, Marras WS, Davis KG. Variations in spinal load and trunk dynamics during repeated lifting exertions. Clinical Biomechanics, 1999, 14:367-375.
This study looked at repeated lifting from a workplace perspective. The intent was to quantify the “variability in lifting motions, trunk moments, and spinal loads.” Comparisons were made between healthy college students and experienced warehouse workers. The authors designed the study to manipulate weight (30 and 60 pounds), box position (anterior and 60 degrees right), and lifting speed (preferred and faster). They combined EMG, motion, and force plate data to create a spinal load model.
The results, in some cases, were consistent with expectations. Velocity of movement was slower with the heavier load. Heavier loads produced greater spinal loading. When the weight was on the side, more lateral and transverse plane motion occurred. However, there were some unexpected findings when comparing groups. Experience in lifting did not decrease spinal loading. When lifting the same weight, the warehouse workers had “greater peak trunk moments” and “greater spinal compression,” as well as greater motion in the frontal and transverse planes. One of the most important findings (contrary to expectations) was that instead of decreased variability with repeated trials, the experienced lifters showed greater variability!
The results of this study and others on variability challenge the traditional notion that variability in movement is undesirable. Certainly, when learning a new skill, variability reduces as the body learns to capture all the forces (both external and internal) to accomplish the task or movement. But this leads to a perspective that performing a movement the “correct” way, over and over again, is representative of a higher level of function. The increased variability demonstrated by experienced lifters in this study, as well as in other studies (i.e. expert jugglers), demonstrates that when task performance reaches the “skilled” level, variability is a good thing. It may spread the tissue stress to different areas, preventing breakdown and symptoms. But it also represents more robust success in that activity, allowing completion of the task in different environments.
Whether the goal is reducing tissue stress or expanding success or both, practitioners of Applied Functional Science® (AFS) recognize that once our patient / client accomplishes a movement as intended, the training or rehab program must be tweaked to promote the variability seen in “expert” performers. The Performance System in 3DMAPS® (3D Movement Analysis & Performance System) and the Certification in Applied Functional Science® (CAFS) provides specific options for tweaking movements. With multiple options, movement practitioners can select the options that “force” the client’s movement system to coordinate the body’s resources in different ways to accomplish the same movement task. Making the movement success more robust is essential.
But what does “robust” mean? How can this be accomplished? In this context, “robust” means resistant to factors that could lead to failure. External factors can be drivers in the environment that can change such as ground surface, gravitational torque, mass, momentum, and friction. Internal factors can be multiple tasks, initial body position relative to gravity, muscle fatigue, and cognitive distractions. If the task needs to be resistant to these factors, then they must be included in a training program to promote variability.
To be more practical, let’s use hitting a low volley in tennis as the task. If we start with the squat as a required component, how can we tweak the squat to promote variability. At Gray Institute®, the AFS Nomenclature, which allows the description of any movement, also suggests appropriate Strategies. If we work on a squat to improve the player’s ability to get down to the ball, then we want to make this new resource more robust. The feet can be in a stride position with either one in front of the other. The feet can be wider or narrower than normal. The feet can be turned in or turned out. Combining these tweaks in each of the three planes will produce 27 different foot position options in which to perform the squat.
To make the squat more authentic, the client should be reaching out with a racket. But they need to reach forward, to the right, and to the left. Varying the direction of the reach changes the position of the trunk, which results in different gravitational torques on the body that must be controlled. The direction of the head driven by the eyes watching the ball also should be incorporated into “robust” training. There is also the momentum of the body moving forward to get to the ball. A program of shuffles (in different directions) and then squats builds variability and authenticity. Even the friction of the playing surface can be different (clay courts), which might require a tweak of the training surface.
There are so many variables to consider. But each variable is a program tweak waiting to be used. Practitioners of AFS recognize the need to train variability, and they embrace all the options to be utilized in order to individualize their programs and maximize patient / client success.
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